Emergent Softening and Stiffening Dictate Transport of Active Filaments

Active semiflexible filaments are crucial in various biophysical processes, yet insights into their single-filament behavior have predominantly relied on theory and simulations, owing to the scarcity of controllable synthetic systems. Here, we present an experimental platform of active semiflexible filaments composed of dielectric colloidal particles, activated by an alternating electric field that induces contractile or extensile electrohydrodynamic (EHD) flows. Our experiments reveal that contractile flow generating filaments undergo softening, significantly expanding the range of accessible conformations, whereas filaments composed of extensile flow monomers exhibit active stiffening. By independently tuning filament elasticity and activity, we demonstrate that the competition between elastic restoring forces and emergent hydrodynamic interactions along the filament governs conformational dynamics. Crucially, we discover that the timescale of conformational dynamics directly governs transport behavior: enhanced fluctuations promote diffusion while stiffening facilitates directed propulsion of nonlinear filaments. Together, our direct visualization studies elucidate the links between inherent filament properties, microscopic activity, and emergent transport while establishing a versatile experimental platform of synthetic filamentous active matter.